1. Field of the Invention
The invention relates to a drying drum assembly for a sheet handling apparatus and a method for the production thereof.
2. Description of Background Art
In high capacity printing systems (>200 sheets per minute) the proper drying of freshly printed sheets is critical. After leaving the print head the ink on the sheets is wet and able to contaminate parts of the printing system or other sheets by contact. These wet sheets cannot be stacked or flipped for duplex printing, but need to dry first. Therefore, after printing, the sheets are transported towards a sheet handling apparatus with a rotatable drying drum, against the outer surface of which the sheets are temporarily adhered. The drum can is heated e.g. by infrared lights, to speed up the drying process. Since the drum rotates the sheet flow is not interrupted, allowing for a continuous printing process. After drying the sheets disengage from the drum and are transported towards for example a stacking unit or redirected to the print head to be duplex printed on their blank sides.
Such a rotary drum has an outer peripheral wall with openings formed therein. A circumferential screen is provided over the outer surface of the drum. The screen comprises perforations. A suction system controls a flow of air through the openings of the drum and the perforations of the screen to attract sheets towards the peripheral wall of the drum, such that the sheets can be removably fixed to the screen.
Due to the heating applied for drying the sheets, the screen and drum also become heated. Since the drum and screen are often formed of different materials, differences in thermal expansion can result in releasing the screen from the drum. To prevent this release such screens are glued securely to the drum.
Drawback of the above described sheet handling apparatus is that the screen cannot be easily replaced. Additionally, the production of such a sheet handling apparatus is relatively complex.